This invention relates to high performance magnetic tape recorder systems and in particular to a high performance tape transport and cartridge.
High performance magnetic tape recorders have been devised for recording and reproducing various types of signals, such as audio signals, analog instrumentation signals and digital data signals. All such recorders must position the tape accurately with respect to a transducer head, must accurately control tape speed, and must maintain uniform tape tension. In many applications they must also be capable of very high acceleration and deceleration rates and very high tape speeds. In some, the capability of recording and reproducing signals in both directions of tape movement is important. The relative importance of these virtues differs from application to application, so that a recorder designed for digital data acquisition, where search speed and data packing densities may be of greatest interest, represents a different design compromise from an instrumentation recorder designed for precise speed control and low flutter at each of several selectable speeds.
Presently known high performance tape recorder systems are complex and expensive. A standard tape transport includes a pair of reels, on which a tape is would, and a transducer (record or reproduce head) between the reels. A motor-driven capstan pulls the tape across the transducer at a uniform speed. The reels are mounted on tensioning motors which drive the reels in opposition thereby establishing tension in the tape and winding the tape in a roll on the takeup reel. Because the amount of tension generated in the tape by the reel motors and capstan is dependent on the constantly changing size of the tape roll on each reel, methods have been devised to sense the tension in the span of tape extending across the transducer and to control the reel motors accordingly. One method uses a tension arm to sense changes in tension; moe recent methods use a vacuum column into which a loop of tape is drawn by a constant vacuum. Both of these systems require long spans of tape between reels, require complex circuitry, and inherently involve changes of tension before corrections are made. Nonetheless, they have been widely used in high performance tape drives.
Another system, based on the conventional approach, adds a second capstan on the other side of the transducer heads from the first capstan. Running the capstan on the takeup side faster than the capstan on the supply side provides a tension across the transducer heads which is substantially independent of the tensioning provided by the reel motors. The capstans are driven by individual motors connected electronically to each other and to a timing signal through a servo system. This system requires four motors and complex circuitry to coordinate the speeds of all the motors.
Another approach which has been tried is based on the techniques described in Newell, U.S. Pat. No. 3,370,803 (1968), and Uber, U.S. Pat. No 3,460,781 (1969). These systems utilize a peripheral drive in which coplanar takeup and supply rolls of tape are mounted on precision carriages and are biased into contact with a central drive capstan. The capstan has a resilient surface in driving engagement with both the periphery of the supply roll and the periphery of the takeup rolls, at the point of departure of tape from the supply roll and at the point of tape arrival at the takeup roll. Tape tension is generated by biasing the takeup roll into contact with the capstan with greater force than applied to the supply roll, thereby causing a differential deformation in the resilient surface of the motor-driven capstan, hence a difference in peripheral speeds of the supply and takeup rolls. A peripheral drive system has the practical advantage that the capstan squeegees out air which otherwise becomes trapped between layers of tape in the takeup roll, and it therefore produces hard-packed tape rolls. The tension generated in the tape, however, is highly dependent on the uniformity of the elastomeric properties of the capstan. It is also dependent on the precise geometry of the capstan-tape roll interface. Therefore, in practical systems the tension generated is dependent on such variables as inhomogeneities in the elastomer, the size of the tape rolls and the temperature, and the tension is not uniform.
It has long been recognized as desirable to provide a high performance tape system in which the tape rolls are enclosed in a cartridge. Cartridge systems not only eliminate threading the tape from one reel to the other, but provide considerable environmental protection for the tape when it is out of the transport. They also permit the tape to be removed from the system without rewinding the tape.
Attempts made heretofore to produce a truly high performance tape recorder system utilizing tape cartridges have not been completely successful. In large part, their failure has been due to limitations inherently imposed by presently known high performance tape drive systems.
Systems based on conventional tape transports generally require such long spans of tape between reels that tape must be pulled from the cartridge (either manually or by a complex mechanism) to provide proper tape speed and tension control, and to provide proper guidance of the tape span by high precision guides. The openings required in the cartridge for reel drive shafts, capstans, tape pulling devices and the like make complete dust-proofing of the cartridge almost impossible. Most importantly, the performance of these cartridge systems has not generally been as good as the performance of high performance open reel recorders.
Attempts have been made to overcome these shortcomings by basing cartridge systems on something other than a conventional tape transport. Most of these systems, however, have resulted in complex and expensive cartridges. For example, numerous cartridges having coaxial reels have been built and proposed. Tape tension is generated either by dragging the supply reel and driving the takeup reel, or by coupling the two reels by a spring mechanism and driving the tape with a capstan. Neither tensioning scheme is entirely effective, and both increase the complexity and cost of the cartridge. Moreover, accurate and gentle guiding of the tape is difficult or impossible.
Although the peripheral drive systems of the Newell and Uber patents, supra, are not particularly well adapted to the use of cartridges, attempts have also been made to utilize them in a cartridge drive system. Such an attempt is shown in Blackie et al, U.S. Pat. No. 3,526,371 (1970). The cartridge shown in that patent contains two tape reel carriage assemblies and a fixed capstan or idler roller. One of the chief aims of a cartridge tape recorder system is to make the cartridges as simple as possible; the cartridges of this system are expensive and complicated. Another cartridge-type tape transport, ostensibly based on the same drive concept, is shown in Hollingsworth, U.S. Pat. 3,638,880 (FIGS. 6-8). Although the cartridge disclosed in the patent is simple, the system is incapable of high performance. In fact, the system is little more than a conventional system without a capstan. Its tape speed and tape tension therefore vary as the sizes of the tape rolls change.
Still another attempt to produce a high performance cartridge drive system utilizes a cartridge containing tape rolls on fixed axes and an endless band which engages the peripheries of both rolls of tape. The band or the tape is driven by an external capstan. The band is so arranged around support posts that its differential stretch causes the takeup reel to run faster than the supply reel, and thereby tensions the tape. Such a system is shown in Wolff, U.S. Pat. No. 3,861,619 (1975). These systems may utilize a simple transport having a single drive motor and no separate tensioning means. However, the systems have inherent limitations which restrict the degree of performance they can provide. They are subject to objectionable flutter and tension variations caused by non-uniformities in the stretch and frictional characteristics of the tensioning band and by undesired frictional and rotational characteristics of the posts which support the tensioning band. Such systems also require rather complex cartridges, provide limited tensioning forces, are capable of limited acceleration rates and a limited range of speeds, have a limited life, and are of limited adaptability to varied applications.